Systems and methods for implementing virtual switch planes in a physical switch fabric

ABSTRACT

A switching device includes multiple interfaces and a switch fabric. The switch fabric includes switch integrated circuits arranged in a number of stages. Multiple virtual switch planes may be implemented in the switch fabric. Data traffic received at the interfaces is selectively assigned to different ones of the virtual switch planes.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 12/134,237, filed Jun. 6, 2008, now U.S. Pat. No. 8,320,369, which is a continuation of U.S. patent application Ser. No. 10/300,639, filed Nov. 21, 2002, now U.S. Pat. No. 7,397,794, the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to network devices, and more particularly, to systems and methods for implementing virtual switch planes in physical switch fabrics of network devices.

2. Description of Related Art

Conventionally, high bandwidth switch fabrics have used several parallel switch “planes” that each carry a fraction of the total bandwidth. FIG. 1 illustrates a conventional switch fabric 100 with parallel switch planes 120, 125, 130 and 135. Each switch plane may include multiple interconnected switch integrated circuits (ICs) 110-1-110-12 (collectively, 110), with each switch IC employing one of a variety of switch architectures, such as a crossbar switch.

Interface cards 105 interconnect with switch ICs 110 of each of the parallel switch planes (only interconnections to switch plane 1 are shown) and divide the received bandwidth over the n planes of the switch fabric 100 (four planes shown). Each of interface cards 105 may interconnect with a number of ports on the switch ICs 110. If switch fabric 100 must support a total bandwidth B and have P ports, then each of the parallel switch planes must also have P ports, but each switch plane only needs to support a total bandwidth of B/n, where n is the number of planes. The use of parallel switch planes thus makes it possible for switch fabric 100 to support bandwidths much larger than could be supported by a single IC switch, without introducing much complexity.

The number of ports on a single switch plane, however, determines the most cost-effective number of interface cards 105 in a given system. Supporting small system sizes (i.e., smaller than the natural number of ports in a fabric) generally requires wasting ports, or designing a new switch fabric. Thus, a conventional switch fabric 100 cannot be used with systems having a different number of interface cards 105 than the number of ports on switch fabric 100.

Therefore, there exists a need for systems and methods that can enable a given switch fabric to support systems with fewer interface cards than the number of switch ports on the switch fabric, thus, permitting the implementation of smaller scale system sizes.

SUMMARY OF THE INVENTION

Systems and methods consistent with the principles of the invention address this and other needs by implementing multiple virtual switch planes in a physical switch plane of a network device such that the switch fabric can support systems with fewer interface cards than the number of switch ports on the switch fabric. A switch fabric with P ports may, when implemented with S virtual switch planes, connect with P/S interface cards by connecting each interface card to the switch fabric S times. Consistent with the principles of the invention, address re-mapping tables may be used within switch ICs of the switch fabric to direct incoming data units through appropriate virtual switch planes to reach destination output interfaces. The use of virtual switch planes within the switch fabric can be transparent to the interface cards, localizing changes to the switch fabric itself rather than requiring the interface cards to be configured differently depending on the switch configuration.

One aspect consistent with principles of the invention is directed to a method of forwarding data units through a plurality of virtual switch planes. The method includes implementing a virtual switch plane in a physical switch plane, wherein the physical switch plane includes input ports and a switch fabric. The method further includes allocating at least one of the input ports to the virtual switch plane and forwarding data units through the at least one allocated input port to the virtual switch plane.

A second aspect consistent with principles of the invention is directed to a method of implementing multiple virtual switch planes in a physical switch plane in which the physical switch plane includes a switch fabric and queues. The method includes segmenting the physical switch plane into the multiple virtual switch planes. The method further includes segregating the queues into groups such that each group of queues is associated with a different one of the multiple virtual switch planes.

Another aspect consistent with principles of the invention is directed to a method of handling data traffic at a physical switch plane of a network device, where the physical switch plane includes virtual switch planes. The method includes receiving the data traffic and selectively assigning the received traffic to different ones of the virtual switch planes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, explain the invention. In the drawings,

FIG. 1 is a diagram of a conventional multi-plane switch fabric;

FIG. 2 is a diagram of an exemplary network device in which systems and methods consistent with the principles of the invention may be implemented;

FIG. 3 is a diagram of components of a first exemplary switch plane according to an implementation consistent with the principles of the invention;

FIG. 4 is a diagram of components of a second exemplary switch plane according to an implementation consistent with the principles of the invention;

FIG. 5 is a diagram of an exemplary switch IC consistent with the principles of the invention;

FIG. 6 is a diagram of exemplary next port and jump tables stored in the switch IC of FIG. 5 consistent with the principles of the invention;

FIGS. 7A and 7B are diagrams of exemplary jump tables consistent with the principles of the invention;

FIG. 8 is a diagram of an exemplary destination fabric output port table consistent with the principles of the invention;

FIG. 9 is a diagram of an exemplary source interface table consistent with the principles of the invention; and

FIGS. 10-11 are flowcharts of an exemplary data unit handling process according to an implementation consistent with principles of the invention.

DETAILED DESCRIPTION

The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents.

Systems and methods consistent with the principles of the invention include mechanisms for implementing virtual switch planes in a physical switch plane of a network device. Through the use of virtual switch planes, the physical switch plane can support systems with fewer interface cards than the number of switch ports on the switch fabric without wasting ports, thus, enabling the implementation of cost effective smaller scale system sizes.

Exemplary Network Device

FIG. 2 is a diagram of an exemplary network device 200 in which systems and methods consistent with the principles of the invention may be implemented. Network device 200 may receive data units, such as packets, from a physical link (not shown). Network device 200 may process the data units to determine destination information and transmit the data units on one or more links in accordance with the destination information. A data unit refers to any type of data, including, for example, packets, cells, datagrams, fragments of packets, fragments of datagrams or cells, or a combination of these types of data.

Network device 200 may include input interfaces 205, a switch fabric 210, and output interfaces 215. Input interfaces 205 may receive incoming streams of data units and send each received data unit to the switch fabric 210 for routing to an appropriate output interface of output interfaces 215. Switch fabric 210 may include multiple physical switch planes (not shown), each of which may include a network of switch ICs that route data units from input interfaces 205 to appropriate output interfaces 215.

Exemplary Switch Fabrics

FIGS. 3 and 4 illustrate exemplary components of a single physical switch plane, implemented with virtual switch planes, of network device 200 consistent with the principles of the invention. FIG. 3 illustrates one exemplary embodiment in which queues associated with the different virtual switch planes are segregated. FIG. 4 illustrates another exemplary embodiment in which the queues are shared by the different virtual switch planes implemented in the single physical switch plane.

As shown in FIG. 3, a single physical switch plane of a switch fabric 210 may include 16 switch ICs 320-1-320-12 (collectively, 320) arranged in a three stage (stage 1 305, stage 2 310, stage 3 315) Clos configuration. Input interfaces 205 may include multiple interface (I/F) cards 325-1-325-4 (collectively, 325) that interconnect with stage 1 305 switch ICs 320. Output interfaces 215 may include multiple I/F cards 325-1-325-4 that interconnect with stage 3 315 switch ICs 320. Each line shown interconnected between one of I/F cards 325 and a switch IC 320 may represent a connection, such as a copper or fiber connection, to ports on the switch ICs 320. FIG. 3 illustrates two virtual planes A and B implemented in physical switch fabric 210. Each of I/F cards 325 may interconnect to a switch IC 320 via a number of connections (two shown for illustrative purposes). Some of the connections between I/F cards 325 and switch ICs 320 may be part of virtual switch plane A and others of the connections may be part of virtual switch plane B. In each stage 1 305 switch IC 320, for example, data units received via the first connection may only be “sprayed” to the first two of stage 2 310 switch ICs 320 (designated “A”). Data units received via the second connection may only be “sprayed” to the second two of stage 2 310 switch ICs 320 (designated “B”). At stage 2 310, two of switch ICs 320 (designated “A”) carry only data units for virtual switch plane A and the other two of switch ICs 320 (designated “B”) carry only traffic for virtual switch plane B.

Virtual switch planes A and B use distinct queues throughout switch fabric 100. At stage 1 305 and stage 2 315, each virtual switch plane uses a separate subset of the input and output ports of each switch IC. At state 2 310, virtual switch plane A and B use separate switch ICs 320, and virtual switch plane A and B further use distinct queues such that virtual switch plane A data units travel only through the first two input ports of each stage 3 315 switch IC 320 and virtual switch plane B data units travel only through the second two input ports of each stage 3 315 switch IC 320. Implementing virtual switch planes in physical switch fabric 210 may, thus, require that an equal fraction of stage 1 305 switch IC 320 input ports be used for each virtual switch plane. In the exemplary embodiment of FIG. 3, in which two virtual switch planes (A and B) are implemented in switch fabric 210, half of the input ports of each stage 1 305 switch IC 320 may be used for virtual switch plane A and the other half for virtual switch plane B. The ports of stage 3 315 switch ICs 320 may have similar constraints. The principles involved in dividing switch fabric 100 into two, virtual switch planes, as described above, may be generalized to divide switch fabric 100 into more than two switch planes.

FIG. 4 illustrates another exemplary embodiment consistent with the principles of the invention in which data units handled by both virtual switch plane A and virtual switch plane B share the same queues in stage 2 310 switch ICs 320 (designated “A+B”). In this exemplary embodiment, stage 1 305 switch ICs 320 spray data units from all input ports to all output ports. Stage 2 310 switch ICs 320 direct data units to the correct stage 3 315 switch IC 320 based on an interface card destination address and virtual switch plane number associated with each data unit.

Exemplary Switch IC

FIG. 5 illustrates an exemplary one of switch ICs 320 consistent with the principles of the invention. The switch IC 320 may include N inputs ports 505-1-505-N (collectively, 505) and N output ports 515-1-515-N (collectively 515) interconnected with switch logic 510. Switch logic 510 may include, for example, crossbar switch logic. Switch logic 510 forwards each data unit received from an input port 505 to an appropriate output port 515 based on the data unit's destination I/F card 325. Each output port 515 may further include one or more queues 520 for buffering data units received from switch logic 510 before sending the data units out of switch IC 320.

Exemplary Next Port and Jump Tables

FIG. 6 illustrates an exemplary next port table 605 and jump table 610 consistent with the principles of the invention. A different next port table 605 and jump table 610 may be associated with each input port 505 of stage 1 305 switch ICs 320. Next port table 605 may map an interface destination address to an output port address of a stage 1 305 switch IC 320. Jump table 610 may map the output port address from next port table 605 to a next port value (NEXT_PORT) that may overwrite the original value in next port table 605. Changing the value in next port table 605 as each interface destination address is mapped allows a sequence of data units, with the same interface destination address, to be load balanced (or “sprayed”) over a set of output ports. The entries in jump table 610 determine the sequence of output ports to use for spraying.

In a switch fabric 210 with two virtual planes, tables 605 and 610 for stage 1 305 input ports 505, associated with virtual plane A, may be programmed to spray data units only to stage 1 305 output ports 515 for virtual plane A. This may be accomplished by storing the value ((i+1)mod p/2) in jump table 610 entry i, where p is the number of ports. Also, the initial values in next port table 605 should be less than p/2. For virtual plane B, the corresponding input ports should have jump table 610 entries set to (((i+1)mod p/2)+p/2) and the initial next port table 605 values may be greater than or equal to p/2. The pointers in jump table 610, thus, form two disjoint circular lists, and each next port table 605 value points to a current position in one of the disjoint lists (i.e., the one corresponding to the virtual plane on which the data units were sent). A sequence of data units sent to a given destination may, therefore, cycle through only half of the output ports corresponding to the virtual plane on which the data units were sent. This algorithm may be generalized for any number of virtual planes.

As shown in FIG. 6, next port table 605 may map an interface destination address associated with a data unit to an output port 515 of stage 1 305 switch IC 320 that receives the data unit from an input interface 205. The interface destination address may correspond to a destination I/F card 325 of output interfaces 215 and may be included in a header of a data unit. An interface destination address received at next port table 605 may be used to index the table to retrieve an output port address (OUTPUT_PORT) of stage 1 305 switch IC 320 through which the data unit should be forwarded. The entire address, part of the address, or the result of an algorithm performed on the address, such as a hash, may be used as the index value. The output port address (OUTPUT_PORT), corresponding to an output port 515, may be passed to jump table 610. The output port address (OUTPUT_PORT) may then index jump table 610 to retrieve a port address (NEXT_PORT) that may replace the previously retrieved entry of next port table 605. A sequence of port addresses (NEXT_PORT) in jump table 610 determines the order in which data units are “sprayed” out the different output ports 515 of stage 1 305 switch IC 320.

FIGS. 7A and 7B further illustrate exemplary embodiments of jump table 610 consistent with the principles of the invention. The exemplary jump table 610 of FIG. 7A may be used in the exemplary switch fabric 210 of FIG. 3. The exemplary jump table 610 of FIG. 7B may be used in the exemplary switch fabric 210 of FIG. 4.

In the exemplary jump table 610 of FIG. 7A, a group of port addresses may be associated with each virtual switch plane implemented in physical switch fabric 210. For example, FIG. 7A illustrates port addresses NEXT_PORT_1A through NEXT_PORT_NA associated with virtual plane A. Data units processed by virtual switch plane A may, thus, be “sprayed” out output ports 515 of stage 1 305 switch IC 320 according to the sequence of entries corresponding to each virtual switch plane.

In the exemplary jump table 610 of FIG. 7B, the port addresses may not be associated with any virtual switch plane. Each data unit, therefore, may be “sprayed” out an output port 515 of a stage 1 305 switch IC 320 according to the sequence of entries of jump table 610 regardless of which virtual switch plane is handling the data unit.

Exemplary Destination Fabric Address Translation Table

FIG. 8 illustrates an exemplary destination fabric address translation table 800 consistent with the principles of the invention. A different table 800 may be associated with each input port 505 of stage 1 305 switch ICs 320. Destination fabric address translation table 800 may map interface destination addresses 805 associated with each data unit to switch fabric output ports 810. Each retrieved fabric output port 810 may correspond to an output port 515 of stage 3 315 switch ICs 320. Each interface destination address 805 associated with a data unit may index table 800 to retrieve a fabric output port address 810 (FABRIC_OUTPUT_PORT) associated with an output port 515 of a stage 3 315 switch IC 320.

In a fabric without virtual switch planes each interface card connects to a single port of each fabric plane. Therefore, each interface card has one destination address. When an interface card sends a packet into the fabric the interface card also transmits the fabric port address of the data unit's destination. In a fabric with virtual switch planes each interface card connects to more than one port of each fabric plane. In order to avoid changes to the interface card configuration depending on the presence or number of virtual planes, ideally the interface card should still have only one “logical” fabric address that is used by the other interface cards to identify a particular card. However, within a switch plane each card has multiple “physical” fabric addresses, one per virtual plane.

The fabric address translation table 800 re-maps the logical fabric destination address provided by the source interface card into a physical fabric address specific to a virtual plane. Because there is a different fabric address translation table 800 associated with each input port, and each input port is associated with a single virtual plane, multiple virtual planes can be supported by loading different values into each fabric address translation table.

Exemplary Source Fabric Address Translation Table

FIG. 9 illustrates an exemplary source fabric address translation table 900 consistent with the principles of the invention. A different source fabric address translation table 900 may be associated with each input port 505 of stage 3 315 switch ICs 320. Source fabric address translation table 900 may map fabric source addresses 905 to a logical source address 910 associated with each virtual plane implemented in physical switch fabric 210. Fabric source address 905 may be automatically constructed by recording the sequence of switch IC 320 ports along the path traveled by a data unit through the stages of switch fabric 210. When the data unit arrives at a stage 3 315 switch IC 320 input port 505, table 900 may be used to re-map the fabric source address 905 to a logical source address used by the I/F cards 325 of output interfaces 215. Source fabric address translation table 900 may map physical source addresses used internally in the fabric to logical source addresses used externally by the interface cards. In a system with virtual planes, multiple physical addresses map to a single logical address so multiple entries in the table will have the same logical address.

Exemplary Data Unit Handling Process

FIGS. 10-11 are flowcharts of an exemplary process for handling data units received at network device 200 in accordance with implementations consistent with the principles of the invention. The exemplary process may begin with the receipt of a data unit at an I/F card 325 of input interfaces 205 [act 1005]. The receiving I/F card 325 may then determine an interface destination address, associated with a destination I/F card 325 of output interfaces 215, and pass the received data unit to a stage 1 305 switch IC 320 [act 1010]. Stage 1 switch IC 320 may index next port table 605, with the determined interface destination address, to retrieve a stage 1 305 switch IC 320 output port (OUTPUT_PORT) [act 1015]. Stage 1 switch IC 320 may further index jump table 610 with the retrieved stage 1 305 switch IC 320 output port (OUTPUT_PORT) to retrieve a next port value (NEXT_PORT) [act 1020]. Stage 1 switch. IC 320 may write the retrieved next port value (NEXT_PORT) into the same entry of next port table 605 [act 1025].

Stage 1 switch IC 320 may then index destination fabric output port table 800 with the determined destination interface destination address to retrieve a fabric output port (FABRIC_OUTPUT_PORT) [act 1030]. Stage 1 switch IC 320 may then send the data unit out an output port 515 corresponding to the retrieved output port (OUTPUT_PORT) value [act 1035]. A stage 2 310 switch IC 320 may then receive the data unit [act 1105]. The stage 2 310 switch IC 320 may send the received data unit out through an output port 515 corresponding to an interface card 325 interface destination address determined by a stage 1 switch IC 320 (FABRIC_OUTPUT_PORT) [act 1110]. A stage 3 315 switch IC 320 on the path through switch fabric 210 may receive the data unit [act 1115]. The stage 3 315 switch IC 320 may index source fabric address translation table 900 with a fabric source address 905 to retrieve a logical source address [act 1120]. Stage 3 315 switch IC 320 may then use the interface destination address determined by a stage 1 switch IC (FABRIC_OUTPUT_PORT) to send the data unit to a corresponding I/F card 325 of output interfaces 215 [act 1125]. The logical source address retrieved from table 900 may be transmitted to the I/F card 325 along with the data unit.

CONCLUSION

Consistent with the principles of the present invention, multiple virtual switch planes may be implemented in a physical switch plane of a network device such that the network device switch fabric can support systems with fewer interface cards than the number of switch ports on the switch fabric. A switch fabric with P ports may, for example, when implemented with S virtual switch planes, connect with P/S interface cards by connecting each interface card to the switch fabric S times. Address re-mapping tables may, consistent with the principles of the invention, be used within switch ICs of the switch fabric to direct incoming data units through appropriate virtual switch planes to reach destination output interfaces. The use of virtual switch planes within the switch fabric can be transparent to the interface cards, localizing changes to the switch fabric itself rather than requiring the interfaces cards to be configured differently depending on the switch configuration.

The foregoing description of preferred embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, though the switch plane described above employed a three-stage Clos network, smaller switch plane implementations that have, for example, a single crossbar chip per physical fabric plane, may be used. In such an implementation, source fabric address translation table 900 and destination fabric address translation table 800 may be implemented in the same IC.

While series of acts have been described in FIGS. 10-11, the order of the acts may vary in other implementations consistent with the present invention. Also, non-dependent acts may be performed in parallel.

No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used.

The scope of the invention is defined by the claims and their equivalents. 

What is claimed is:
 1. A device comprising: a switch fabric including: a physical switch plane including: a group of switch ports, the group of switch ports including a first quantity of switch ports,  the physical switch plane implementing a group of virtual switch planes, and  the group of virtual switch planes including a second quantity of virtual switch planes, and the switch fabric connecting each switch port, of the group of switch ports, to one of a group of interface cards,  the group of interface cards including a third quantity of interface cards,  each interface card, of the group of interface cards, including the second quantity of connections to the physical switch plane, and  the third quantity being less than the first quantity; and a group of queues, each virtual switch plane, of the group of virtual switch planes, being associated with a respective queue of the group of queues, and a received data unit, determined to be associated with a virtual switch plane, of the group of virtual switch planes, being buffered in the respective queue associated with the virtual switch plane.
 2. The device of claim 1, where the switch fabric is to: use a separate subset of switch ports, of the group of switch ports, for a respective virtual switch plane of the group of virtual switch planes.
 3. The device of claim 1, where the switch fabric is to: transfer data units associated with a first virtual switch plane, of the group of virtual switch planes, through the switch fabric using only a first subset of the group of switch ports, and transfer data units associated with a second virtual switch plane, of the group of virtual planes, through the switch fabric using only a second subset of the group of switch ports, where switch ports, included in the first subset of the group of switch ports are not included in the second subset of the group of switch ports.
 4. The device of claim 1, where the switch fabric is to: forward the received data unit through the switch fabric via the virtual switch plane, and buffer the received data unit in the respective queue as the received data unit is being forwarded through the switch fabric.
 5. The device of claim 1, where the switch fabric is to: identify an interface card, of the group of interface cards, associated with the received data unit, associate an identifier with the received data unit based on the identified interface card, determine that the received data unit is to be forwarded through the switch fabric, via the virtual switch plane, based on the identifier, and forward the received data unit through the switch fabric via the virtual switch plane.
 6. The device of claim 1, where the switch fabric further includes: a plurality of switch circuits, a first set of the plurality of switch circuits comprising an ingress stage, a second set of the plurality of switch circuits comprising an intermediary stage, and a third set of the plurality of switch circuits comprising an egress stage, where the group of virtual switch planes are implemented in each of the first set of the plurality of switch circuits.
 7. The device of claim 1, where the switch fabric further includes: switch circuits arranged in an ingress stage, an intermediary stage, and an egress stage, where each interface card, of the group of interface cards, includes the second quantity of connections to each switch circuit of the switch circuits arranged in the ingress stage.
 8. The device of claim 1, where the switch fabric further includes: a plurality of switch circuits arranged in a three-stage configuration.
 9. The device of claim 8, where the three-stage configuration comprises a Clos configuration.
 10. A method comprising: implementing, by a device, a set of virtual switch planes in a physical switch plane, the physical switch plane including a set of switch ports; connecting, by the device, each switch port, of the set of switch ports, to a respective interface card of a set of interface cards, a quantity of interface cards, included in the set of interface cards, being less than a quantity of switch ports included in the set of switch ports, and each interface card, of the set of interface cards, including a quantity of connections, to the physical switch plane, that is equal to the quantity of virtual switch planes included in the set of virtual switch planes; and forwarding, by the device, data received via the set of interface cards through the switch fabric via the physical switch plane using the set of virtual switch planes; forwarding the data including: determining that a data unit, included in the data received via the set of interface cards, is associated with one of the set of virtual switch planes, and the device including in a set of queues, each virtual switch plane, of the set of virtual switch planes, being associated with a respective queue of the set of queues, and the data unit being buffered in the respective queue, associated with the one of the set of virtual switch planes, when the data unit is forwarded through the switch fabric.
 11. The method of claim 10, further comprising: associating each subset, of a plurality of separate subsets of the set of switch ports, with each virtual switch plane of the set of virtual switch planes.
 12. The method of claim 10, where forwarding the data through the switch fabric further includes: transferring data units associated with a first virtual plane, of the set of virtual switch planes, through the switch fabric using only a first subset of the set of switch ports, and transferring data units associated with a second virtual plane, of the set of virtual planes, through the switch fabric using only a second subset of the set of switch ports.
 13. The method of claim 10, where the set of queues includes a quantity of queues equal to a quantity of virtual switch planes.
 14. The method of claim 10, where the device includes: a first set of switch circuits forming an ingress stage of the physical switch plane, a second set of switch circuits forming an intermediary stage of the physical switch plane, and a third set of switch circuits forming an egress stage of the physical switch plane; and where implementing the set of virtual switch planes includes: implementing the set of virtual switch planes in each of the first set of switch circuits forming the ingress stage of the physical switch plane.
 15. The method of claim 10, where the device includes: a first set of switch circuits forming an ingress stage of the physical switch plane, a second set of switch circuits forming an intermediary stage of the physical switch plane, and a third set of switch circuits forming an egress stage of the physical switch plane; and where connecting each switch port, of the set of switch ports, to the one of the set of interface cards causes each interface card, of the set of interface cards, to have a quantity of connections to each switch circuit, of the first set of switch circuits forming the ingress stage of the physical switch plane, that is equal to the quantity virtual switch planes included in the set of virtual switch planes.
 16. A device comprising: a switch fabric including: a physical switch plane, a group of virtual switch planes being implemented in the physical switch plane; and each switch port, of a group of switch ports, of the physical switch plane, being connected to a respective interface card, of a group of interface cards of the device, the group of interface cards including a quantity of interface that is less than a quantity of switch ports, and each interface card, of the group of interface cards, including a quantity of connections to the physical switch plane that is equal to a quantity of virtual switch planes; and a group of queues connected between a plurality of switch circuits included in the physical switch plane, each virtual switch plane, of the virtual switch planes, being associated with a respective queue of the group of queues.
 17. The device of claim 16, where a separate subset of the switch ports is assigned to each of the virtual switch planes.
 18. The device of claim 17, where a group of received data units is associated with one of the virtual switch planes, and where the group of received data units is forwarded through the switch fabric using the separate subset of the switch ports assigned to the one of the virtual switch planes.
 19. The device of claim 16, where a received data unit is associated with one of the virtual switch planes, and where the received data unit is buffered in the respective queue associated with the one of the virtual switch planes when the received data is forwarded through the switch fabric.
 20. The device of claim 16, where an interface card, of the group of interface cards, is associated with a received data unit, where an identifier is associated with the received data unit based on the interface card, and where a virtual switch plane, of the virtual switch planes, for forwarding the received data unit through the switch fabric is determined based on the identifier, and where the received data unit is forwarded through the switch fabric via the determined virtual switch plane. 